Recording the Sun

One of my favourite things at Jodrell Bank is the crystal ball on the roof of the Control Building.

Don’t worry, I’ve not gone all Mystic Meg. It’s a Campbell-Stokes Recorder – a glass sphere which focuses the sunlight onto a card held behind it, burning a trace measuring the hours of sunshine. The sky in this close-up photo is cloudy, sadly a fairly common occurrence for the northwest of England, but the video below shows the recorder in the act of burning a hole in the equinoctial card.

Luckily the Lovell Telescope, inverted and distorted by the glass sphere in the photo, works at radio wavelengths of around a few cm and so can see through the clouds.